update cadence (open-telemetry#1047)

* update cadence

* update every other

Author: cartersocha

README.md

@@ -67,8 +67,8 @@ keeping it up to date for you.
 ## Contributing
 
 To get involved with the project see our [CONTRIBUTING](CONTRIBUTING.md)
-documentation. Our [SIG Calls](CONTRIBUTING.md#join-a-sig-call) are Mondays at
-8:15 AM PST and anyone is welcome.
+documentation. Our [SIG Calls](CONTRIBUTING.md#join-a-sig-call) are every other
+Monday at 8:30 AM PST and anyone is welcome.
 
 ## Project leadership